They probably won't explode from pressure caused by altitude. They may however break open from having heavier bags thrown on top of them. Luggage is not generally handled gently, but more often thrown from place to place. If you must pack liquid make sure it is double baged in a ziplock type bag and prefferably in a hardsided container to protect from crushing. Any leaks could not only get your bags wet but other suitcases around yours.